The use of spinal rods is conventional for correction of spinal trauma or conditions, such as curvature of the spine. Generally, an orthopedic stabilization system may include a pair of spinal rods that are coupled to a bone or bones. The rods are generally contoured and longitudinally disposed adjacent to vertebral bodies of a spine.
In some cases, a pair of spinal rods are fastened in parallel on either side of the spinous process. The assembly can be significantly strengthened by using at least one additional stiffening member known as a transverse connector or cross link to horizontally connect the pair of spine rods. A number of different transverse connectors are known. Generally, the transverse connectors should provide strength and control torsion. Stresses can act to return a stabilized bone system to a deformed position. For example, stresses on a spine and on a spinal stabilization system often operate to return a corrected spine to a deformed position. Transverse connectors can inhibit rod movement of the spinal stabilization system during a post-operative period so that the spine remains in a corrected position.
Rods of an orthopedic stabilization system can be aligned along a longitudinal axis of the spine generally parallel to each other on each side of the midline of the spine. Due to a wide variety of factors, two rods are rarely three dimensionally geometrically aligned. That is, two rods very rarely are located a uniform distance from each other along their entire length. Generally, the two rods have some convergence or divergence in the medial-lateral direction. The two rods may also not have the same orientation with respect to the coronal plane. The rods might also not have a coplanar geometry from a lateral view.
To address the variations of geometrical alignment, surgeons sometimes will bend the rods to accommodate a transverse connector or bend the transverse connector to accommodate the rods. In addition, transverse connectors have been developed that have some adjustability to adapt for variations from geometrical alignment. Two piece transverse connectors allow for the stabilization of rods that are oriented in different horizontal and vertical planes. Further, the connection between multi-shaft transverse connectors must resist shear to avoid separation and provide stability to the rods.
Because of the forces acting along the transverse connector and the movement of the spinal rods, the connection between the transverse connector and the rod must be secure to avoid movement of the transverse connector along the spinal rod. Some rod fastening systems of transverse connectors use threaded fasteners to attach the transverse connector to adjacent rods. The threaded fastener can be a set screw or a nut. Not tightening a threaded fastener enough may allow movement of the transverse connector. Overtightening a threaded fastener could result in damage to the system and failure of the transverse connector.
Installation of a spinal fixation device is a lengthy and complicated surgical procedure. Simplification of the assembly of the device will tend to reduce the complications associated with the procedure.